This invention pertains to a special wellhead electrical insulating connector for electrode wells used for electrical heating of a subsurface viscous oil bearing formation. More particularly, this invention concerns an iron base metal and ceramic insulating connector wherein the outer surface of the ceramic and the inner surface of the metal are joined by heat shrink fitting with an intermediate layer of high expansion, softer, stress controlling nonferrous metal.
In the recovery of oil from viscous oil bearing formations it is usually possible to produce only a very small portion of the original in-place oil by natural or primary production which relies solely on the natural forces present in the formation. A variety of artificial recovery techniques, therefore, have been employed to increase oil recovery. It has been proposed, for example, in U.S. Pat. Nos. 3,642,066; 3,874,450; 3,848,671; 3,948,319; 3,958,636; 4,010,799 and 4,084,637, to use electrical power to add heat to a subsurface pay zone containing tar sands or viscous oil to render the viscous hydrocarbons more flowable. In general, two or more electrodes are connected to an electrical power source and are positioned at spaced apart points in contact with the earth in a manner such that when electric current is passed between the electrodes it will heat visocus oil in the subsurface formation. Voltages of 200 volts and up to and exceeding 1000 volts are applied to the electrodes. Currents up to 1800 amperes are passed between electrode wells. Most of the heat generated by power consumption in or near the formation occurs in and adjacent to the electrode well and heat transfer outward into the formation by conduction is slow. This leads to temperatures up to and possibly exceeding 500.degree. F. This heat is conducted by the tubing and casing to the wellhead of the electrode wells. The wellhead fittings, therefore, must be capable of safely withstanding these elevated temperatures.
In subsurface electrical heating processes whether or not the electricity is flowed through the casing tubing, the voltages and currents used cause power leakage flow and discharge to surface equipment if standard wellhead electrical isolating devices are employed. Standard wellhead electrical isolating devices have closely spaced metal parts and thin electrical insulating material. The space between the metal parts is easily shorted by debris, chemicals and the products of corrosion. The electrical paths around the electrical insulation allow power leakage and sometimes act as power consuming resistance paths which generate heat at the wellhead. It would, therefore, be desirable to provide a reliable wellhead connector that reduces power leakage losses and does not provide resistance paths that act like an electrical resistance heater. It is an object of this invention to provide a wellhead connector which acts as an electrical insulator. It is a further object of this invention to describe an insulating connector for a wellhead of an electrode well used in electrically heating a subsurface formation in which extreme stresses are relieved or prevented and other stresses are better controlled. It is still a further object of this invention to provide an insulating connector that will safely withstand temperatures up to and exceeding 500.degree. F.